FIG. 1 is a structural diagram of a cellular wireless communication system, which, as shown in FIG. 1, is mainly comprised of a User Equipment (UE), an access network and a Core Network (CN). A network comprised of eNodeBs (eNBs), or comprised of eNBs and eNB controllers is referred to as a Radio Access Network (RAN), which is responsible for transactions of an access layer, such as radio resource management. Physical or logical connections may exist between the eNBs, and each eNB can be connected to more than one core network nodes. The core network is responsible for transactions of a non-access layer, such as location update, etc. The core network is an anchor point of a user plane. The UE refers to various devices, such as mobile phones or laptop computers, etc., which can communicate with cellular wireless communication network.
In the cellular wireless communication system, wireless coverage of a fixed eNB network is limited due to various reasons, for example, block of wireless signals by various building structures causes coverage leak existing in the coverage of the wireless network. On the other hand, at edge regions of a cell, attenuation of wireless signal strength and interferences between adjacent cells results in poor communication quality of the UE when being at edges of the cell and rise of the error rate of wireless transmission. In order to improve the coverage rate of data rate, group mobility, temporary network deployment, throughput at edge regions of the cell and coverage of a new area, a scheme is provided for introducing a wireless network node, which is referred to as a relay, in the cellular wireless communication system.
The relay is a station which relays data between other network nodes through a wireless link and can control information functions, and is also referred to as a relay node/relay station. FIG. 2 is a structural diagram of a cellular wireless communication system containing a relay. As shown in FIG. 2, the UE which is served directly by the eNB is referred to as a macro UE, and the UE which is served by the relay is referred to as a relay UE. Interfaces between various network elements are defined as follows: a direct link is a wireless link between the eNB and the UE, including an uplink/downlink (DL/UL) direct link; an access link is a link between the relay and the UE, including a DL/UL access link; and a backhaul link is a wireless link between the eNB and the relay, including a DL/UL backhaul link.
The relay may relay data by various methods, such as directly amplifying a received radio signal transmitted by the eNB; or processing, such as demodulating or decoding, data transmitted by the eNB accordingly after receiving the data, and then forward the data to the UE, or the eNB and the relay cooperatively transmitting data to the UE, and conversely, the relay will also relay the data transmitted from the UE to the eNB.
Among many types of relay, characteristics of one type of relay will be described as follows: the UE can not distinguish cells under the relay from those under the fixed eNB, i.e., from the perspective of the UE, the relay itself is a cell and has no difference from the cell under the eNB. Such cell can be referred to as a relay cell. The relay cell has its own Physical Cell Identity (PCI), and transmits broadcast like ordinary cells. When the UE resides in the relay cell, the relay cell can individually allocate and schedule radio resources to the UE for use, and can be independent of radio resource scheduling of the eNB participating in the relay. The eNB to which the relay is connected through a backhaul link is referred to as a Donor NodeB/eNodeB (DNB/DeNB). The interface and protocol stack between the relay cell and the relay UE are the same as those between an ordinary eNB cell and an ordinary UE.
FIG. 3 is a structural diagram of a LTE based cellular wireless communication system. As shown in FIG. 3, the LTE system uses an Internet Protocol (IP) based flattened architecture, and is comprised of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), an Evolved Packet Core (EPC) node and other support nodes. The EPC node includes a Mobility Management Entity (MME), a Serving Gateway (S-GW) and a Packet Data Network Gateway (P-GW). The MME is responsible for control plane signaling, including control plane related operations, such as mobility management, non-access layer signaling processing, user mobility management, context management, etc; and the S-GW is responsible for transmitting, forwarding, routing handoff of UE user plane data. The eNBs are logically connected to each other via an X2 interface, which is used to support the mobility of the UE within the entire network to ensure seamless handoff of the user. The P-GW is a node which connects the EPC with a packet data network, such as Internet, and is responsible for allocating an IP address of the UE, filtering IP data packets by service type into service data flows and binding the service data flows to a corresponding transmission bearer, and so on.
Each eNB is connected to a System Architecture Evolution (SAE) core network via a S1 interface, i.e., is connected to the MME via a control plane S1-MME interface, is connected to the S-GW via a user plane S1-U interface. The S1 interface supports multipoint connections between the eNB and the MME and S-GW. The MME and the S-GW are connected via a S11 interface, the S-GW and the P-GW are connected via a S5 interface and can also be combined into one network element, and at this point, the S5 interface does not exist. The eNBs are connected with each other via an X2 interface. Each eNB transmitting signaling and data to the UE via an Uu interface (which is originally defined as a wireless interface between the UTRAN and the UE). After the relay is introduced, the wireless interface between the relay and the eNB is an Un interface, and the interface between the relay and the UE is the same as that between the eNB and the UE and thus is also an Uu interface.
Usually, operators deploy relays for several reasons, such as lack of terrestrial transmission resources, or a single relay cannot satisfy requirements of extensive or long distance network layout and can only be deployed around an eNB having terrestrial transmission resources when the terrestrial transmission cannot operate in the event of a disaster or the mobile cellular network is deployed rapidly in a short time. Therefore, in order to solve the problem of deployment scope, the concept of multiple hops is introduced, i.e., after accessing the eNB, the relay can further continue to act as an access node of subsequent relays, so as to form a multi-hop structure.